Optimal design of PCM in internal walls for nZEB buildings

The implementation of phase change materials PCMs in the building sector has been recently regarded as a valuable strategy in order to achieve nearly Zero Energy Buildings. If properly employed in the internal partition, the PCM layer can increase the thermal storage capacity of the building with consequent reductions of air-conditioning energy requirement. Furthermore, an adequate thermal mass of internal walls can help in attenuating the indoor air temperature drop consequent to the shutdown of the air-conditioning system in winter condition as well as attenuating a temperature rise in summer. These aspects are amplified in highly-glazed buildings, where owing to the solar radiation entering through the glazed surfaces, the surface temperatures of the internal walls are highly variable and it is thus possible to exploit the phase change. In this study, the energy performances of highly-glazed buildings with PCM integrated in the internal walls were evaluated by a parametric analysis conducted by means of dynamic numerical simulations. A modular two-story reference building, with a highly glazed external envelope, located in Rome was investigated considering three different typologies of external opaque walls, different volumes of PCM integrated in the internal walls and several values of melting temperature in the summer and winter seasons. The simulations were conducted with the aim to assess the thermal energy requested for heating and cooling and to determine a temperature deviation index to quantify the ability of PCM to maintain the indoor air temperature at acceptable levels, when the system is not operating. The results of the analysis showed, both in insulated and non-insulated buildings, in which conditions in a warm Mediterranean climate, the phase change materials can mitigate the energy demand associated with the building air conditioning and temperature deviation in the environments when the system is switched off.